The invention relates to perpendicular magnetic recording media, and more particularly, relates to a soft magnetic underlayer of such media.
Perpendicular magnetic recording systems have been developed for use in computer hard disc drives. A typical perpendicular recording head includes a trailing write pole, a leading return or opposing pole magnetically coupled to the write pole, and an electrically conductive magnetizing coil surrounding the yoke of the write pole. Perpendicular recording media may include a hard magnetic recording layer with vertically oriented magnetic domains and a soft magnetic underlayer to enhance the recording head fields and provide a flux path from the trailing write pole to the leading or opposing pole of the writer. Such perpendicular recording media may also include a thin interlayer between the hard recording layer and the soft underlayer to prevent exchange coupling between the hard and soft layers.
To write to the magnetic recording medium, the recording head is separated from the magnetic recording medium by a distance known as the flying height. The magnetic recording medium is moved past the recording head so that the recording head follows the tracks of the magnetic recording medium, with the magnetic recording medium first passing under the opposing pole and then passing under the write pole. Current is passed through the coil to create magnetic flux within the write pole. The magnetic flux passes from the write pole tip, through the hard magnetic recording track, into the soft underlayer, and across to the opposing pole.
In addition, the soft underlayer helps during the read operation. During the read back process, the soft underlayer produces the image of magnetic charges in the magnetically hard layer, effectively increasing the magnetic flux coming from the medium. This provides a higher playback signal.
Perpendicular recording designs have the potential to support much higher linear densities than conventional longitudinal designs due to a reduced demagnetizing field in the recording transitions. In addition, the described bilayer medium is used in perpendicular recording to allow increased efficiency of the recording head. The soft magnetic underlayer of the perpendicular recording medium forms inverse image charges and substantially magnifies both the write field during recording and the fringing field of the recorded transition during reproduction. The quality of the image, and therefore the effectiveness of the soft underlayer, depends upon the permeability of the soft underlayer.
To support the high image efficiency, the soft underlayer should be in an unsaturated state. However, during recording a top portion of the soft underlayer is likely to be saturated. Therefore, thickness and magnetic saturation induction, Bs, of the soft underlayer needs to be matched to appropriate parameters of the recording head. Magnetic saturation of the soft underlayer causing the permeability reduction will result in write field degradation. Therefore, the soft underlayer should be relatively thick and have a high magnetic saturation induction, e.g. Bs greater than 1 Tesla.
However, one of the challenges of implementing perpendicular recording is to resolve the problem of soft underlayer noise. The noise may be caused by fringing fields generated by magnetic domains, or uncompensated magnetic charges, in the soft underlayer that can be sensed by the reader. For example, soft underlayer materials, such as Ni80Fe20 or Co90Fe10, may exhibit multi-domain states that produce noise enhancement in the read-back signals, hence, degrading the signal-to-noise (SNR) ratio. If the magnetic domain distribution of such materials is not carefully controlled, very large fringing fields can introduce substantial amounts of noise in the read element. Not only can the reader sense the steady state distribution of magnetization in the soft underlayer, but it can also affect the distribution of magnetization in the soft underlayer, thus generating time dependent noise. Both types of noise should be minimized.
In addition, magnetostatic interaction between the soft underlayer and the hard layer can degrade SNR ratio and reduce linear density.
There is identified a need for perpendicular magnetic recording media with a soft magnetic underlayer that overcomes limitations, disadvantages, or shortcomings of known perpendicular magnetic recording media.
The invention meets the identified need, as well as other needs, as will be more fully understood following a review of this specification and drawings.
In accordance with an aspect of the invention, a perpendicular magnetic recording medium comprises a hard magnetic recording layer and a soft magnetic underlayer under the hard magnetic recording layer. The soft magnetic underlayer comprises a first ferromagnetically coupled multilayer structure and a second ferromagnetically coupled multilayer structure. The soft underlayer also includes a coupling layer that is positioned between the first and second multilayer structures for antiferromagnetically coupling the multilayer structures to one another. Each multilayer structure may include first and second magnetic layers that are ferromagnetically coupled by an interlayer positioned therebetween. Each multilayer structure may include additional magnetic layers with interlayers positioned therebetween.
In accordance with yet another aspect of the invention, a magnetic disc drive storage system comprises a housing, a perpendicular magnetic recording medium positioned in the housing and a movable recording head mounted in the housing adjacent the perpendicular magnetic recording medium. The perpendicular magnetic recording medium comprises a hard magnetic recording layer and a soft magnetic underlayer under the hard magnetic recording layer. The soft magnetic underlayer includes a first ferromagnetically coupled multilayer structure, a second ferromagnetically coupled multilayer structure, and a coupling layer positioned therebetween for antiferromagnetically coupling the first and second ferromagnetically coupled multilayer structures.
In accordance with another aspect of the invention, a perpendicular magnetic recording medium comprises a hard magnetic recording layer and a soft magnetic layer under the hard magnetic recording layer. The soft magnetic underlayer includes a plurality of magnetic layers and a plurality of interlayers individually interposed between each of the plurality of magnetic layers in order to antiferromagnetically couple each of the plurality of magnetic layers successively.
In accordance with a further aspect of the invention, a method of making a laminated magnetically soft underlayer of a perpendicular magnetic recording medium is provided. The method includes depositing a first ferromagnetically coupled multilayer structure on a substrate. The method also includes depositing a coupling layer on the first ferromagnetically coupled multilayer structure. The method also includes depositing a second ferromagnetically coupled multilayer structure on the coupling layer, wherein the coupling layer serves to antiferromagnetically couple the first and second multilayer structures. The step of depositing the first ferromagnetically coupled multilayer structure on a substrate may include depositing an interlayer on the substrate, depositing a magnetic layer on the interlayer, depositing an additional interlayer on the magnetic layer, and depositing an additional magnetic layer on the additional interlayer. The step of depositing a second multilayer structure on the coupling layer may include depositing a magnetic layer on the coupling layer, depositing an interlayer on the magnetic layer, depositing an additional magnetic layer on the interlayer, and depositing an additional interlayer on the additional magnetic layer.